In the proposed project I plan to investigate and further characterize the RNA metabolism of cells infected with RNA tumor viruses. Most of the experiments will involve mouse cells infected with murine leukemia virus (MuLV), and in specific cases other cells and other RNA tumor viruses will be used. Virus-specific RNA in these experiments will be detected by RNA-DNA hybridization of cellular RNA with virus-specific DNA synthesized by the "endogenous" reverse transcriptase reaction in MuLV. Five topics will be studied: (1) The sequence complexity of MuLV virion RNA will be determined by studying the annealing kinetics of MuLV RNA and DNA in comparison to annealing kinetics of other RNA species of known molecular weight. (2) Virus-specific RNAs from non-producer cells and cells with partial virus expression will be identified and characterized by annealing cellular RNA with H3 DNA probe. (3) Labelling kinetics of virus-specific RNA in MuLV infected cells will be studied and characterization of rapidly-labelled virus-specific RNA will be performed. These RNAs will be isolated by hybridization to excess virus-specific DNA attached to cellulose. The labelled RNA will be eluted and analyzed while the DNA cellulose will be regenerated and reutilized. (4) Virus-specific RNA at different times after infection will be studied. In order to do this, we will attempt to develop a system of synchronous infection. (5) We will attempt to idnetify intracellular virion precursor particles in producer cells. This will be carried out by looking for virus-specific RNA in large ribonucleoprotein particles and further characterizing these particles.